c.1300, "at a disadvantage;" mid-14c., "in times past;" late 14c., "in or to the rear;" see arrears. Meaning "behind in duties or payments" is from 1620s.
mid-14c., "in times past," from Old French ariere "behind, backward," from Vulgar Latin *ad retro, from Latin ad "to" (see ad-) + retro "behind" (see retro-). Meaning "balance due" dates from early 15c.; phrase in arrears first recorded 1610s, but in arrearages is from late 14c.